Radio receiver



March 6, 1962 J. R. BANKER 3,024,360

RADIO RECEIVER Filed Nov. 12, 1958 Clock Mechanism Converter Ampllfler WITNESSES INVENTOR John R. Banker ATTORNEY United States Patent 3,024,360 Patented Mar. 6, 1962 Fine 3,024,360 RADIO RECEIVER John R. Banker, Plainfield, N .J., assignor to W estinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 12, 1958, Ser. No. 773,505 3 Claims. (Cl. 250-20) The present invention relates to a radio receiver employing an audible alarm circuit, and more particularly to an alarm clock-radio combination wherein the alarm signal is produced by the audio circuits and sound reproducing means of the radio receiver.

The usual arrangement for providing an alarm signal in clock-radio combinations is to provide the clock with the usual alarm clock type of buzzer or bell mechanism. Such arrangements are unnecessarily expensive in that two separate sound producing devices, to wit, the clock bell and the radio loudspeaker, are provided.

In copending patent application Serial No. 737,673 filed May 26, 1958, entitled Radio Receiver Apparatus, by Alden F. MacDonald, and assigned to the present assignee, there is described a clock-radio combination which includes a feedback circuit operatively associated with the audio network of the radio receiver to provide an audible alarm tone at the loudspeaker in response to the actuation of a control switch by the clock mechanism. While the arrangement of the above-mentioned application is highly satisfactory and economical as compared tothe usual alarm clock bell mechanism, it has the disadvantage that the feedback network causes the resistance coupled audio circuits to operate somewhat like a multivibrator with the amplitude oscillation being limited in the audio amplifier and with the output waveform being nonsinusoidal and containing many harmonic components. Such an output signal produces a raucous tone at the loudspeaker which may be extremely unpleasant to the ear. To avoid undesirable tones, critical adjustment of the audio circuits have been necessary, resulting in added expense of manufacture, assembly, and adjustment of the radio receiver.

Accordingly, it is an object of the present invention to provide a radio receiver having an alarm clock and capable of producing a pleasant sounding alarm tone.

It is another object of the present invention to provide a radio receiver having means to produce an audible alarm signal which is pleasing to the ear and which may be adjusted in amplitude without disturbing the musical tone of the signal.

It is a further object of the present invention to provide a radio receiver in which an audio frequency alarm tone is produced at the sound reproducer by regeneration in the audio circuits of the receiver and in which the musical character of the alarm tone is substantially independent of normal variations in the electrical constants of the audio circuits.

A different object of the present invention is to provide a clock-radio receiver combination having an alarm signal producing means featuring great economy of structure and circuitry.

The foregoing and other objects of the present invention will be apparent from the following description taken in accordance with the accompanying drawing, which drawing forms a part of this application, and in which the single figure is a circuit schematic of a preferred embodiment of the invention.

Referring now to the drawing, the radio receiver is assumed to be a superheterodyne broadcast receiver for reception of signals in the usual 550 to 1700 kilocycles band. Persons skilled in the radio art are thoroughly familiar with various desirable designs for such a receiver.

It is to be understood that my invention is independent of the frequency band of the receiver, the type of the receiver or the nature of the carrier wave modulation. For example, the invention may be applied to a frequency modulated (PM) carrier wave receiver, as well as to the usual amplitude modulated type receivers. The receiver is provided with a conventional antenna 10 connected to a converter 11 which is in turn connected to apply intermediate frequency signals to a conventional intermediate amplifier 12. The output of the IF amplifier 12 is applied through a conventional 1F transformer 17 to one diode of a diode-triode discharge device 13, which may be a conventional 12AV6, and which serves as a demodulator and first audio amplifier stage. Specifically, the upper end of the IF transformer secondary winding is connected to the anode of the diode section of tube 13. The lower end of the transformer secondary winding is connected to ground through a volume control potentiometer 15. An intermediate frequency bypass capacitor 19 is connected from the upper end of potentiometer 15 to ground. The slider of potentiometer 15 is connected through a coupling capacitor 14 to the control electrode of the triode section of tube 13. The cathode of tube 13 is connected to ground and the anode is connected through a load resistor 20 to the positive terminal B+ of a source of direct current 46. A resistor 16 is connected between the control electrode of tube 13 and ground. Audio signals are derived in the demodulator section of tube 13 and are applied by way of potentiometer l5 and capacitor '14 to the control electrode of the triode section of tube 13. The amplified audio signals are applied from the plate of tube 13 through a coupling capacitor 24 to the control electrode of a second audio amplifier 25 which may be a conventional pentode power amplifier such as the SOCS type. The control electrode of tube 25 is connected to ground by a grid resistor 26, across which is shunted an intermediate frequency bypass capacitor 27. The cathode of discharge device 25 is connected to its anode by a high frequency bypass capacitor 23, and a cathode biasing resistor 28 is connected from the cathode to ground. The screen grid of tube 25' is connected to 3+ in the conventional manner. The anode of tube 25 is connected to the upper end of the primary winding of a conventional output transformer 31 with the lower end of the primary winding being connected to B+ in the usual manner. The secondary winding of output transformer 31 is connected in series with an adjustable resistor 33 to the voice coil of a conventional loudspeaker type sound reproducer 32. The variable resistor 33 is shunted by a switch member 34a, the function of which will appear as this description proceeds.

In order to provide tone frequency oscillation of the audio network at a predetermined tone frequency, a feedback network is coupled between the output circuit of the audio amplifier and its input circuit. More specifical ly, the feedback circuit includes a coupling capacitor 35, a conductor 42, and difierentiating capacitor 36 connected serially between the anode of discharge device 25 and the control electrode of discharge device 13. A control switch 34b is connected between the conductor 42 and ground. With the controlswitch 34b in the open position as shown in the drawing, feedback is applied from the anode of tube 25 through capacitors 35 and 36 to the control electrode of tube 13 so that the audio amplifier comprising the triode section of tube 13, tube 25, and the feedback network will oscillate so long as switch 34b is open. With switch 34b in the closed position, the conductor 42 is shorted to ground so that no feedback to the grid of tube 13 is available. Under that circumstance, tubes 13 and 25 operate as a conventional audio amplifier 3 network to translate audio signals from the demodulator to the sound reproducer 32.

As stated heretofore, energizing voltage for the tubes and 13 is provided from the positive terminal B+ of a direct-current power source 46 having its negative terminal connected to ground in accordance with conventional practice. Alternating current for energizing power source 46 is supplied from the usual 117 volt line. In series with one side of the alternating-current line connection to the power supply 46 there is provided a switch 43 of a clock mechanism 44. In accordance with conventional practice, the driving motor of the clock mecha' nism has a pair of input terminals 44a and 44b which are connected directly to the alternating-current line voltage source. When the clock switch 43 is actuated by the arrival of a time for which the clock has been preset the rectifier type power supply 46 will be energized to apply B+ voltage by way of conductor 48 to the circuits of tubes 13 and 25. The audio circuits will then be energized to produce either an alarm signal or radio intelligence depending upon the preset position of switch 34b. Switches 34a and 34b are ganged together and to the slider of volume control potentiometer 15 so that switches 34a and 3411 will be opened only when the volume control is adjusted to the minimum volume position, that is, when the slider of potentiometer 15 is set toward the lower end of potentiometer 15.

The radio receiver system, as thus far described, is substantially similar to that described and claimed in co pending application, Serial No. 737,673, heretofore referred to. The present invention differs in one respect from the aforementioned application in that in addition to the feedback circuit, there is provided a relaxation oscillator circuit means for periodically altering the gain of the audio amplifier network so that the amplitude of the alarm tone signal is modulated in accordance with the frequency of the relaxation oscillator circuit. To that end there is provided a relaxation oscillator means 37 which is connected between the conductor 42 and ground and is operative to periodically apply negative voltage pulses through capacitor 36 to the control electrode of tube 13. More specifically, the relaxation oscillator comprises a resistor 41, a capacitor 38, and a resistor 39 connected serially between B-I- and ground, with capacitor 38 being shunted by a neon bulb or gas tube 40.

In operation, the relaxation oscillator 37 is maintained inoperative so long as switch 34b is closed, and accordingly, the audio amplifier, including tubes 13 and 25, translate audio signal from the demodulator to the sound reproducer 32 in the conventional manner. When switches 34b and 3411 are opened by adjusting the slider of the potentiometer 15 to the minimum volume position, voltage is applied from B+ through resistor 41 to the upper end of capacitor 38. Capacitor 38 charges at a rate depending upon the RC constant of the series circuit including capacitor 38 and resistors 39 and 41. When the charge on capacitor 38 reaches a predetermined magnitude, the neon tube ionizes to suddenly dissipate the charge on capacitor 38. The structure of relaxation oscillators are well known to those skilled in the electronic arts, and accordingly, further description of the operation of oscillator 37 is unnecessary. It is to be understood, however, that the present invention is independent of the type of oscillator circuit which is utilized, and while a relaxation oscillator has been shown and described by way of example, it is to be understood that various other oscillators and pulse generator circuits may be utilized within the scope of the present invention. The essential criterium for the oscillator circuit means 37 is that it apply periodic negative going pulses to conductor 42.

In the example shown, such negative going pulses appear across resistor 41 each time that neon tube 40 becomes ionized. The negative going pulses are translated through capacitor 36 and drive the control electrode of tube 13 negative, thereby biasing off tube 13 and temporarily interrupting the regenerative oscillation in the audio frequency circuits. The negative pulses appearing at conductor 42 are ditferentiated by the action of capacitor 36 and resistor 16, and hence the negative pulses at the control electrode of tube 13 are of short duration as compared to the period of the relaxation oscillator 37. As the negative bias at the control electrode of tube 13 decays through resistor 16, regenerative oscillation in the audio network is resumed and continues until neon tube 40 again becomes ionized. Thus the tone frequency oscillation applied to the sound reproducer 32 is modulated in amplitude in accordance with the periodicity of the relaxation oscillator 37.

Switch 34a and variable resistor 33 provide a means for adjusting or varying the amplitude or loudness of the audible alarm signal at the sound reproducer 32. With switch 34a in the open position, resistor 33 may be adjusted to provide any desired level of alarm signal. With switch 34a in the closed position resistor 33 is inoperative and the volume of the radio intelligence signals may be controlled by volume control potentiometer 15.

In the preferred embodiment of the present invention, capacitor 35 is selected to provide the desired amount of audio frequency feedback. Capacitor 36 provides isolation of the control grid of tube 13 from the direct-current voltages appearing in the relaxation oscillator. Capacitor 36 further cooperates with resistor 16 to differentiate the pulses applied to the control grid of tube 13. The values of capacitor 38 and resistor 41 determine the frequency of the relaxation oscillator 37. Resistor 39 is provided to prevent the feedback signal from passing to ground through capacitor 38. The values of capacitors 29, 35 and 36 and resistor 39 determine the natural oscillatory frequency of the audio circuits and feedback network. Accordingly, they determine the frequency of the alarm tone signal applied to sound reproducer 32.

Although it is not intended to limit the present invention to any specific circuit parameters, the following components have been found suitable for an arrangement in accordance with the embodiment shown.

Tube 13 12AV6 Tube 25 SOCS Resistor 39 megohm l Capacitor 38 microfarad .02 Resistor 41 megohms 22 Capacitor 29 microfarad .02 Capacitor 36 micromicrofarads 390 Resistor 16 "megohm 6.8 Capacitor 35 mmf 15 Resistor 33 ohms- 47 While the present invention has been shown in one embodiment only, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit and scope thereof.

I claim as my invention:

1. In a clock-radio combination, an audio amplifier having an input circuit and having an output circuit, sound reproducing means coupled to said output circuit for producing sound in response to audio signals translated through said amplifier, a feedback circuit coupled between said output circuit and said input circuit for causing oscillation of said amplifier at a predetermined tone frequency to produce an audible signal at said sound reproducing means, switch means connected to control the application of energizing voltages to said amplifier, clock mechanism coupled to said switch means for closing the same at preselected times, a relaxation oscillator coupled to said amplifier for periodically reducing the gain of said amplifier and feedback circuit so that said tone frequency signal is modulated in accordance with the oscillatory frequency of said relaxation oscillator,

and a manually operable control switch for preselectively enabling and disabling said feedback circuit so that said sound reproducing means emits oscillatory tone signals at said preselected time when said feedback means is enabled and emits sound intelligence corresponding to received radio waves when said feedback means is disabled.

2. In an alarm-clock radio combination, means for receiving sound modulated radio waves including a de modulator, an audio amplifier and a sound reproducer coupled in cascade in the order named, a feedback circuit connected to said amplifier for providing regenerative feedback oscillation therein at a predetermined tone frequency thereby to cause an audible alarm signal to be emitted from said reproducer, a relaxation oscillator including a gas discharge tube and having a frequency less than said tone frequency connected to said feedback circuit for modulating the loop gain of said amplifier and feedback circuit so that said alarm signal varies in amplitude at the frequency of said relaxation oscillator, switch means connected to control application of energizing voltages to said amplifier and said relaxation oscillator, a clock mechanism including presettable means coupled to said switch means for closing the same at a preselected time thereby to cause sound emission from said reproducer, and manually operable switch means connected to said feedback circuit for selectively disabling and enabling the same thereby preconditioning said receiving means respectively to reproduce the sound modulation of said radio waves and to produce said audible alarm signal.

3. In an alarm-clock radio combination, means for receiving sound modulated radio waves including a demodulator, an audio amplifier and a sound reproducer coupled in cascade in the order named, manually adjustable volurne control means coupled between said demodulator and said amplifier, a feedback circuit connected to said amplifier for providing regenerative feedback oscillation therein at a predetermined tone frequency thereby to cause an audible alarm signal to be emitted from said reproducer, a relaxation oscillator having a frequency less than said tone frequency connected to said feedback circuit for modulating the loop gain of said amplifier and feedback circuit so that said alarm signal varies in amplitude at the frequency of said relaxation oscillator, switch means connected to control application of energizing voltages to said amplifier and said relaxation oscillator, a clock mechanism including presettable means coupled to said switch means for closing the same at a preselected time thereby to cause sound emission from said reproducer, and switch means ganged with said volume control means to operate upon adjustment for minimum sound volume and connected to said feedback circuit for selectively disabling the same thereby preconditioning said receiving means to produce said audible alarm signal only when said volume control means is adjusted to the minimum sound volume position.

References Cited in the file of this patent UNITED STATES PATENTS 2,040,439 Langer May 12, 1936 2,304,095 Hull Dec. 8, 1942 2,361,585 Appel Oct. 31, 1944 2,367,327 Beers Jan. 16, 1945 2,870,325 Sanger Jan. 20, 1959 2,882,390 Kuhl et al. Apr. 14, 1959 FOREIGN PATENTS 580,905 Great Britain Sept. 24, 1956 264,468 Switzerland Jan. 3, 1950 

